Virtually since the invention of the internal combustion engine, people have been trying to increase efficiency and lower emissions. Two common categories of internal combustion engines are spark ignition and compression ignition (as used herein, the phrase “compression ignition” includes, but is not necessarily limited to: Diesel/Stratified Charge Compression Ignition (SCCI), Homogeneous Charge Compression Ignition (HCCI), Homogenous Compression Ignition (HCl), Homogeneous Charge with Spark Ignition (HCSI), Gas Direct Compression Ignition (GDCI), diesel and other fuels, as well as fuel blends, carbureted and/or injected as different types of fuel and fuel blend compression ignition, spark-assisted ignition, fuel-assisted ignition, etc.).
Spark ignition engines utilize a spark from a spark plug to ignite the combustion process of the air-fuel mixture within the combustion chamber of the engine. In contrast, compression ignition engines utilize temperature and density increases in the air-fuel mixture within the combustion chamber to auto-ignite the combustion process. Spark ignition engines typically have much lower efficiency than compression ignition engines. Because the flame propagates from the point of ignition (i.e. the spark), it results in incomplete combustion. In compression ignition engines, no flame front exists, instead because the combustion is initiated by increased pressure, the ignition is uniformed, and/or takes place, within multiple places within the combustion chamber, causing nearly simultaneous/instant ignition throughout the entire air-fuel mixture and resulting in more complete combustion. Conventional compression ignition engines must be carefully designed to provide for combustion just before top dead center, taking into account the timing of the fuel injected (typically, direct injected to control combustion cycle) into the combustion chamber, to avoid catastrophic damage to the engine if combustion occurs too early.
Due to the nearly instantaneous ignition of the entire air-fuel mixture within the combustion chamber of a compression ignition engine, an enormous amount of pressure is created within the combustion chamber all at once, as opposed to the more gradual increase in pressure that would be created as the flame propagates through the combustion chamber of a spark ignition engine. This immediate pressure increase is particularly high in homogeneous charge compression ignition (HCCI) engines. As such, engine manufacturers have been required to carefully control compression ignition engines such that the ignition occurs when the piston of the engine is at top dead center or moving down from top dead center. Otherwise, if the ignition occurs before the piston reaches top dead center, catastrophic engine failure will result (i.e. including, but not limited to, bent piston rods, collapsed piston skirts, blown head gaskets, etc.). Nevertheless, such precise control requirements necessitate extremely tight design parameters, limiting compression ratio and/or operating temperature for such engines. Too high a compression ratio can result in auto-ignition before top dead center. Reducing compression ratio, however, increases the temperature required to achieve auto-ignition, thus making the engine difficult to run in cold temperature environments.
U.S. Pat. No. 6,557,520 to Roberts, Jr., the entire disclosure of which is incorporated herein by reference, discloses a multi-zoned combustion chamber and method for combustion control in compression ignition engines that helps to control the immediate combustion pressure surge created in a compression ignition engine. Roberts, Jr. physically segregates the combustion chamber into multiple smaller, sealed, chambers (e.g. a primary chamber and at least a secondary chamber, as well as possibly a tertiary, or more subsequent chambers) through a stepped shaped design of the piston and cylinder head. Specifically, referring to FIG. 1, Roberts, Jr. discloses a cup-shaped piston 140 that has a central recess 141 surrounded by a circumferential protruding wall 142 portion of the piston. The cylinder head 132 of Roberts, Jr. is configured to matingly receive the cup-shape of the piston and has a central protuberance 133 surrounded by a circumferential recess 134. The central recess 141 of the piston is adapted to slidingly receive the central protuberance 133 of the head, and the circumferentially protruding wall 142 is adapted to be slidingly received between the piston cylinder 130 and the central protuberance 133 and the recess 134. FIGS. 2-8 illustrate the multiphase sequence of the internal combustion processes of the engine of Roberts, Jr., in which combustion is initiated in the primary chamber 143 while delaying combustion in the secondary chamber 144.
FIG. 2 illustrates a first phase, which begins after a normal induction stroke, in which air is introduced into the combustion chamber 146. Fuel is delivered and mixed into the combustion system through valve 41 and/or fuel injector 62.
FIG. 3 illustrates a later, second phase in the compression stroke of the combustion chamber 146. This phase illustrates the initiation of chemical reactions within the unburned fuel/air masses 150, 151 in the primary chamber 143 and the secondary chamber 144 due to compression heating. At this phase, the combustion chamber 146 is separated into two individual combustion chambers (the primary chamber 143 and the secondary chamber 144) due to the design and motion of the piston and the design of the combustion chamber.
FIG. 4 illustrates a third phase where the fuel/air mass 150 trapped within the primary chamber 143 undergoes a compression ignition process. When compression ignition is undertaken, rapid combustion of the fuel/air mass 150 in the primary chamber 143 occurs. The size of the primary chamber 143 modulates the amount of energy trapped in the primary chamber 143 so that when the fuel/air mass 150 ignites, the pressure and temperature that is achieved can be controlled through design. The pressure required to ignite the fuel/air mass 150 is a function of thermodynamic interaction. The primary chamber 143 and the secondary chamber 144 have different compression ratio values, so that the fuel/air mass 151 within the secondary chamber 144 will not auto-ignite due to compression from the piston.
FIG. 5 illustrates a fourth phase where the compression ignition process proceeds to a rapid combustion process within the primary chamber 143. Since the primary chamber 143 is being utilized as an ignition control for the secondary chamber 144, the timing after TDC is not necessary.
FIG. 6 illustrates a fifth phase where the fuel/air mass 150 has been converted to a high pressure, high temperature, combusting gas 150A within the primary chamber 143. In Roberts, Jr., the fifth phase occurs after TDC, when the piston 140 is moving in the direction of a down stroke 44. In this fifth phase, the combusting gas 150A continues to expand and remains segregated from the remaining fuel/air mass 151 (or remaining combustible gas) in the secondary chamber 144.
FIG. 7 illustrates a sixth phase where the piston 140 has moved to a predetermined position where segregation of the primary chamber 143 and secondary chamber 144 is eliminated. The sixth phase occurs after TDC, as the piston continues to move in the direction of a down stroke 44. In this phase, combustion of the remaining fuel/air mass 151 in the secondary chamber 144 is initiated. FIG. 7 shows the combusting gas 150A from the primary chamber 143 thermodynamically communicating with the remaining fuel/air mass 151 of the secondary chamber 144 and causing it to be converted into a remaining combusting gas 151A. After the primary chamber 143 and secondary chamber 144 have been desegregated and the combusting gas 150A of the primary chamber 143 is allowed to communicate with the secondary chamber 144, the combusting gas 150A in the primary chamber 143 and the thermodynamic state of the primary chamber 143 is used as the ignition source for the remaining fuel/air mass 151 in the secondary chamber 144.
FIG. 8 illustrates a seventh phase where all of the remaining fuel/air mass 151 of the secondary chamber 144 has been ignited and converted into a combusting gas 151A. Ignition of the secondary chamber can be by compression ignition, direct flame contact, or a combination thereof.
The multi-phase combustion process of Roberts, Jr. allows the combustion process to be initiated by compression caused by the piston, without requiring precise control of the reaction to ensure it occurs when the piston is at or past top dead center. Instead, the segregation of the combustion chamber allows the piston to cause auto-ignition only in the primary chamber, which has a higher compression ratio than the secondary chamber. The relatively small volume of the primary combustion chamber reduces the downward force on the piston, reducing the risk of damage to the engine even if the piston is in its upstroke. The remaining combustion does not occur until the piston is in its down stroke and the seal/barrier (created by the piston and head shape) between the primary and secondary combustion chamber is removed.
Despite the benefits provided by the multi-phase combustion process, the apparatus and method of Roberts Jr. suffer from several drawbacks. For example, the design of the piston central recess 141, and circumferential recess 134 of the head, create trap volume areas in which it is difficult to obtain a homogeneous air-fuel mixture (as used hereafter meaning exhaust, Exhaust Gas Recirculation (EGR), intake air and fuel are all mixed in a homogeneous fashion). This can significantly reduce the performance and efficiency of the engine. In addition, the central recess 141 of the piston lowers the position of the wrist-pin connecting the piston to the rod. Such a design increases likelihood of engine failure due to decreased control of piston cradle rock/piston slap as well as reduced strength at an area of significant stress on the piston. Moreover, the physical seals that are created between the primary and secondary (tertiary, on so on) combustion chambers, compound the difficulty in creating a homogenous air-fuel mixture, making it difficult to control engine knock. Therefore, it would be beneficial to provide systems and methods for achieving multi-phase compression ignition that reduce trap volume, reducing engine knock, and/or decrease likelihood of engine failure, to have control over compression ignition at a multitude of ranges of RPM's, temperatures and/or multiple loads (with and without boost—e.g. supercharge, turbo, etc.).
In addition, the use of compression ignition in “Siamese cylinder” engines has been difficult or impossible to control. “Siamese cylinder” engines are multi-cylinder engines in which the engine cylinders are arranged in such a way that they do not have channels in the cylinder walls between adjacent cylinders for water or other coolant to circulate. Such arrangements are typically used when it is desirable to have an engine block of limited size or when the stability of the cylinder bores is of concern (such as in racing engines). The lack of coolant results in hot spots at the locations in which adjacent cylinders intersect with one another, which makes control of compression ignition difficult. Therefore, it would be beneficial to provide apparatuses, systems and methods for achieving and/or controlling compression ignition (including spark-assisted and/or fuel-assisted compression ignition) in a “Siamese cylinder” internal combustion engine.